Photoelectric registry of strip filters



Oct. 8, 1957 u. E. CONOVER PHOTOELECTRIC REGISTRY OF STRIP FILTERS Filed March 25, 1955 2 Sheets-Sheet l Oct. 8, 1957 u. E. CONOVER PHOTOELECTRIC REGISTRY OF STRIP FILTERS 2 Sheets-Sheet 2 Filed March 25, 1955 INVENTOR. 0mm '5. COA/OI/t'R' United States Patent Ofiice Patented Oct. 8, 1957 PHOTOELECTRIC REGISTRY F srnrr FILTERS Ulmer E. Conover, Sayreville, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application March 25, 1955, Serial No. 496,787

14 Claims. (Cl. 117-211) This invention relates to color television pickup, or camera, tubes. In particular this invention relates to a method of manufacturing target electrodes for color television pickup tubes.

One type of color television pickup tube comprises an evacuated envelope having an electron gun in one end thereof. The electron gun produces an electron beam which scans a target electrode within the other end of the envelope. The target electrode normally comprises a transparent support member having a large plurality of clusters of color filter strips arranged thereon. Each of the clusters of color filter strips includes one color filter strip that passes one of three primary colors. Extending across each of the color filter strips is a different semi-transparent signal strip. Covering all of the signal strips is a photoconductive layer.

In tubes of the type briefly described above, it is desirable to have the color filter strips in contiguous relation, i. e. in contact, so that substantially no light passes between adjacent color filters. This contiguous relationship is desirable in order to prevent white light from passing between the filter strips and actuating the photoconductive layer. Also, it is desirable that each color filter is contiguous to the adjacent color filter, rather than partially extending over an adjacent filter, in order to provide color purity in the output signal.

it is also desirable in tubes of this type to have the semi-transparent signal strips centrally located on their respective color filter strips. If the signal strips are not centrally disposed, they must be made more narrow to prevent electrical shorts between adjacent strips. When the signal strips are centrally located, larger areas of the target may be utilized for picture reproduction since the signal strips may be made wider, and still be electrically insulated one from the other.

In the past, targets of the type described above have been manufactured by evaporating material through a movable mask comprising a plurality of fine grill wires. The grill wires are moved with respect to the transparent target support plate during the formation of the target to put down portions of the signal strips and the filter strips at the proper places. The movement of the Wires relative to the target plate has been measured by means of micrometers. Thus, when a change in location is desired the support plate is moved with respect to the grill wires, by a gear arrangement, until predetermined readings of the micrometers are reached. The micrometer adjustments have been found to be unreliable for several reasons such as, for example, dust particles in the adjustment gearing. The errors in the micrometer adjustments have been found, at times, to be greater than the width of a single color filter strip and much greater than the distance between a pair of signal strips. Other determining factors in inaccurate positioning are the inability of the gear train to repeat settings, and also the physical ability of the Operator to consistently make accurate readings of micrometer settings. The inability of the micrometer to repeat settings is especially pronounced when the step of depositing the signal strips is started. The reason for this is that the masking mechanism must be taken apart to replace one set of grill wires with another set the wires which are of a larger diameter to provide signal strips that are more narrow than the color filter strips. When the set of larger grill wires is used, it must be positioned centrally over the deposited color filter elements.

It is therefore an object of this invention to provide a novel method of manufacturing targets which substantially eliminates errors which occur because of inaccurate mechanical adjustments.

It is a further object of this invention to provide a novel method of determining the center of an extremely narrow color filter strip.

These and other objects are accomplished in accordance with this invention by providing a method of manufacturing a pickup tube target which includes the steps of depositing a first group of color filters spaced apart on a transparent support member; then measuring, by means of photoelectric optical devices, the exact location of the first group of color filters in order to determine the correct position for the second group of color filters; depositing the second group of color filters; then measuring by means of a photoelectric optically device the location of the second group to determine the position of a third group of color filters; and depositing the third group of color filters. When the color filters have been deposited, the exact center of each of the color filters is determined by photoelectric optical means and a different signal strip is deposited on each color filter in the exact center of each of the color filters.

Other features and advantages of this invention will become apparent from the following detailed description when read in conjunction with the accompanying two sheets of drawings wherein:

Figure l is a sectional view of a pickup tube manufactured in accordance with the methods taught by this invention;

Figure 2 is an enlarged fragmentary plan view of the target shown in Figure 1;

Figure 3 is a sectional view taken along line 33 of Figure 2;

Figure 4 is a sectional View of a means for manufacturing the target in accordance with this invention; and

Figure 5 is a perspective view of apparatus utilized to manufacture targets in accordance with this invention.

Although the invention is applicable to various types of devices it will now be described in detail with reference to a color television pickup tube. However, it should be understood that this invention is applicable to other types of devices and particularly to other types of pickup tubes.

Referring now to Figure 1 there is shown a sectional view of a color television pickup tube It? manufactured by methods in accordance with this invention. Pickup tube 10 comprises an evacuated envelope 11 having an electron gun 12 in one end thereof. The electron gun 12 includes the usual cathode 14, control electrode in, and one or more accelerating electrodes 18. A final accelerating electrode 20 is in the form of a wall coating, and is connected to a potential source (not shown) by means including spring fingers 21 which are supported by, but insulated from, the electron gun 12.

An electron beam is produced by the electron gun and is directed toward a target 23 in the other end of the envelope ll. Means are provided for focusing the electron beam, and scanning the beam over the target 23 to form a raster, and may include a focus coil 25, a deflection yoke 27, and an alignment coil 29. A foraminous electrode 31, which is permeable to the electron beam, is positioned adjacent to. target- 23. and-inoperation, together with focus coil 25, functions to insure that the electron beam in its final approach to the surface of target 23, is normal thereto. Thetarget 23", is conventionally supported adjacent to atransparent end of the envelope 11. Terminal pins 33 are sealed through the envelope to connect the target tosources of potential (notshown) and to support the target 23.

The target 23, which is shown in detail in Figures 2 and 3, comprises a transparent support member 35; which may be formed of a separate element as shown, or may be formed by the end of envelopell. The target support member 35 is arranged normal to'the electron beam andhas a pair of' sets-of conductive" strips, or bus bars 7 on the surfacethereof toward the electron beam; Only one set of bus bars 37 is'sli'own; for simplicity of illustration, with the other set being arranged adjacent to an opposite side of supportmember-GSP Spanning the support member 35, substantially transverseto the bus bars--37, is a plurality of color filter" strips39, 40 and" 41. Eachof the color filter-strips is of'aninsulating materialsuchas, zinc selenide, zinc snlphide'or magnesium fluoride and passes one of three primary colors, 6. g.

39 red, 40 blue and 4-1 gre'en'; Centrally located on each of the color filter strips is aseinfitran'sparent conductive signal strip 43. Each ofthe' signal strips 43 is connected to one bus bar 37in each of the sets of bus bars for the particular colorfilterunderconsideration. Covering the signal strips 43'is a photoconductive layer 44, which is shown as partially broken away for simplicity of illustration.- As shown-'by- Figure 2 each of the sig-- nal strips 43is insulated from thebusbars 37 for'the other colors by-ineans of the'el'ectrically insulating color filter strips 40 or 41.

The support'menib'er 35 'may be any transparent mate'- rial such as glass. Bus bars 37 may'bo any/"conductive material, for example gold, which may be deposited by any known means such as evaporation; Due-to-the fact that busbars 37'are remote'from the picture reproduc'- tion areas of target 23, the busbars' 3 7 need not be transparent. Color filter strips 39; 40 and 41 may-he any of the well'known color filters such sis-interference type filters, r dichroic type filters. target shown in Figure 2,. the color filters-39; 40*and 41 are electrically insulating. Thesignal strips- 43"- are made of any highly conductive material and are semitransparent to light. a film of gold which may be'deposited by evaporation. The photoconductive layer-"4'4 may beany material having aspectralresponse similar" to" that of the human eye; one'example of"such'a photoconductive materialis antimony tri-sulphide.

For best operation itis desirable thafea'ch of theeolor" filter strips 39, 40'and 41' be contiguous'with the filter strips that are adjacent thereto.- Also, for optimum tube operation, eachof the signal strips" 43 should'be' centrally'located on its respective color filter" strip 39, 40 or 41. The color filter stripsshould bein' the contiguous relation in orderto eliminate the possibility'of white. or unfiltered, light passing between thecolor filter strips and falling on the photoconductor'to producespurious white signals. Also, for best operation, the color filter strips should notove'rlapwhich would cause color mixing in the picture's'repr'oduced by deVice'IOJ- Theuse ful areas' of the photo-conductor 44" are' the areas directly over a signal strip 43: Therefore, a maximum width of signal strips is-preferrediir order to'providehighv definition to the pictures obtained-from the target. Each of the signal-strips 43, should thus-be centrally located over one of .the': color filters. to providea maximum width to each signal strip,.with sufiicient insulation between adjacent signal strips.

. Referring now to Figures 4 andthere is shown a means for manufacturing targets in'accordance with this invention. Specifically, Figure 4 shows a sectional view In the example of a One material which is suitableis 4: of. an evacuatedbellajar. 46.having anevaporator. crucible 48 supported adjacent to a heater element 50. The bell jar 46 may be evacuated by any well known means, not shown. The crucible 48 includes several pockets 51 which are designed to hold the various materials for making a target 23. The pockets of crucible 48 are selectively located, by means'of'th'e' rotatable arm 49, adjacent to the heater element-'50; for depositing particular materials. Supported above the crucible 48 is an evaporator shield 52' which is designed'to shieldatarget support assembly 54'until' the selected material in" the evaporator has reached the. desired temperature so that the amount of material deposited may be accurately controlled. Target support assembly 54 is shown as being greatly enlarged for purposes of illustration.

The target support assembly includes a frame 56, for holding the target support plate 35, that is movably supported upon a grill wire holder" 58: The holder 58 supports a large-plurality of line grill wires 60. Ar: ranged beneath the grill wii'es 60 isa' shield 62for' determining, by means of the particulara'perture 63, 63, 63" 01"64' selected, the lengthofthe'strip which is to bc evaporated through'apertured shield 62 and through the grill, wires 6th. Thus, strips evaporated through aperture 63 are shorter than's'trips evaporated through larger aperture 63 etc; Asshown in' the drawings; frame 56 is movab'ly supported with respect to the grilliwires 60 asrepresented by the arrow 65. Also; shield 62 is movably supported with'respect to frame 56 as'represented by'arrow 67.

Bus bars 37 are laid down'byevaporating goldthroug'h an appropriate mask onto the target" support late. 35. Next, the target support'plate' 35" is positioned in the support assembly 54"andabove the'grill wire'sft). Then, color filter material ina'pocket 51' is'heated to evaporating temperature, shield 52 is rotated aside, and a first group of color filter strips 39' is deposited by evapcrating the electrically insulating filter materialssfrom thepocket 51 through the grill-wires 60 onto thetarget support plate'35i The color filter strips 39, 40" and 41 arecontiguous with each other in'accordan'ce'with this invention. When the color filter strips arecontiguous, or even when they are-onlyclosely spaced, it has been.foundthat'insulating materialmay be'scatteredfromithe grill Wires 60 into adjacent areasof plate 35. As'an'e'xample, s'orneinsulatenougli'jto aifect' the filtering propertiesof-adjacent" color filters t is enough-to hinder'good electrical connections between-the signal strips and busb'ars for the adjacent filters: Thus, iffcolor fil'ter strip'41'were depositedfirst, nsulatingmaterial therefrom maybe scatteredonto the intermediate bus bar 37 so that a good electrical connection could notbe' made between tlie'interniediate bus bar 37 and the signal strip43for the color filter 40; This harmful 'scatterin'gmay be eliminated by depositing the materials in the following order: short color filter 39,

V then'it's signal strip"43, intermediate color filter 40, and its signal strip 43; and long color filter 41 and itssignal-strip.

This order'of' deposition. eliminates harmful scattering] because of the-large distances involvedbetween adjacent bus bars. 37 as compared to thewshort'distance between a color filterand an adjacent signal strip.- Therefore, when the first group of color filter strips-39 has been deposited, the maskingframe 58'is removedfrom belljars46 and replaced with one-having wires of larger diameter (not' shown) fordepositinga. set-of signal strips 43' on the depositedcolonfilter strips 39. 'When the. grill wires are 1 changedgit is. desirable to accurately align thecentral portionof the color-filter strips39 with the spacingsfespectively between the grid wires of the new mask. This is necessary in order to deposit a signal strip 43 on the center of each filter strip 39.

In accordance with this invention, the center line of the signal strip mask is aligned so that the space between adjacent wires accurately overlies the center line of one color filter strip 39. This alignment is accomplished by reflecting light from a source 64 through the grill wires 60 and through the deposited color filter strips with a mirror 69. The reflected light is directed into a light measuring device 56 including a photocell. The exact alignment of spacings between the grill wires and the center of the deposited color filter strips is found by moving the target support plate 35, over the wire grill mask with a screw thread adjustment 68. Light passing through the grill wires and the glass plate gives a reading on device 66. As the plate 35 is moved over the grill wires, the light transmission through plate 35 is measured by device 66. The light transmitted passes from a maximum to a sharp minimum reading and back to a maximum, as the grill wires are aligned in turn with a clear portion of plate 35, with a portion coated with filter strips 39, and then with a clear portion, respectively. The fact that the light transmission passes to a sharp minimum indicates the point where the spacings between the grill wires are accurately aligned with the center of the corresponding filter strips. The light from source 64 for a particular measurement is light of the monitoring Wave length, i. c. light of a wave length which the filter is designed to reiect. For example, blue-green light is used for red filters 31 green light for blue filters ill, and blue light for green filters With the exact centers of the deposited red color filter located respectively over the centers of the spacings between the grill wires, the signal strips 43 are laid down, by evaporating gold onto the deposited color filter strips 39.

When the s' strips 43 have been deposited on the color filter strips 22?, the grill wires are replaced with the original smaller diameter grill wires so for depositing the second group of color filter strips 40, i. e. blue. in order to accurately locate the second group of color filter strips 4d, the exact center of the deposited strips 39 is found by measuring the minimum light transmission point for the blue-green light as described above. When the exact center of the deposited color filter strips has been found, frame 56 is moved one complete color filter width, i. e. the width of the spacing between adjacent grill wires 60. In a successfully designed target this color filter width is in the order of 1.04 mils. This dimension is not limiting as it should be understood that other widths of color filters may be utilized, as well as color filters of different widths, in accordance with this invention. When frame 56 has been moved the desired amount, a second group of color filter strips is deposited, e. g. blue color filter strips By accurately determining the center of the first deposited group of color filter strips, the second group of color filter strips is accurately deposited in contiguous relationship with respect to each of the color filter strips 39 in the first deposited group of color filter strips.

When the second group of color filter strips 459 has been deposited, the grill wires are replaced and the center of the second group of color filter strips 49 is found by finding the minimum light transmission point for the second group of color filter strips 40, i. e. using the monitoring light of a green color in the example. The center of the color filter strips l-tl is found as described above and signal strips 43 are deposited centrally thereon.

After the two groups of color filter strips have been deposited, e. g. color filter strips 39 and if and their signal strips 4 3, the original grill wires are replaced and the third group of color filter strips is located by moving frame 58 with screw 63 until the maximum light transmission is measured by light passing through the remaining un-coated areas. For this measurement white light is utilized. At this setting of screw 68 no further movement 6 of frame 56 is necessary to deposit the third group of color filter strips 41.

When the maximum light transmission point is found, the third group of color filter strips 41 is deposited at this point. Then the grill Wires are changed and the final group of signal strips 43, i. e. for the green, are deposited at the center of the third group of color filters by measuring the minimum light of the monitoring color, i. e. blue light as described above.

An alternative method of measuring the location of the first group of color filter strips, in order to deposit the second group of color filter strips, is to vary the position of the support plate to the point where the maximum light transmission through plate 35 becomes constant. At this point the spacings between grill wires all are registered with clear areas which are contiguous with the color filters on plate 35. With the frame 55 in this position, the second group of color filters is deposited.

it should be understood that while depositing the first, second and third groups of color filter strips, the apertured shield 62 is positioned so that the correct lengths of each of the groups of color filters is determined by the aperture size selected.

The color filter strips may be deposited before any of the signal strips 43. When this order of deposition is utilized, the location of each of the deposited color filter strips should be determined by this invention before any other group of color filter strips is subsequently deposited. One reason for this is that heat from filament 50 may cause changes in the adjustment mechanism so that predetermined setting of mechanism 63 cannot be depended upon to provide accurate positioning of frame 5'6 so that contiguous filter strips may result.

Even when all of the color filter strips are eposited before any signal strips 43, it is desirable for optimum operation to accurately position the transparent signal strips 43 on the center of each of the color filter strips. The exact center group of the deposited color filter strips is determined in accordance with this invention by determining the maximum light transmission point for the particular color filter under consideration, i. e. using red light for red filters 39', or by using the minimum light transmission point for the monitoring light as described above.

Although the invention has been described as relating to a particular type of target for a television pickup tube, it should be understood that it is equally applicable to other types of targets. Also, the invention need not be limited to a grill but may utilize a foraminous mask in which the apertures are in any arrangement. Furthermore, the invention has utility in putting opaque materials through a mask onto a transparent surface. In such a case the mask is accurately registered over the deposited pattern when the light transmission through the support plate and mask is substantially zero.

What is claimed is:

l. The method of manufacturing a target of t e including a plurality of color filter strips each having a different semi-transparent conductor thereon, said method comprising depositing one of said color fil er strips through a wire grill onto a support plate, determining the center of said one color filter strip by determining a point of minimum light transmission through said filter, moving the grill with respect to said support plate a predetermined amount and depositing the second of said color filters, determining center of the space between said first and said second deposited color filters by determining the maximum light transmission point therebetween, and depositing a third color filter strip onto the center of said space.

2. The method of manufacturing a target of the type including a plurality of color filter strips on a transparent support member and a different conductive signal strip on each of said filter strips, said method comprising the steps of depositing said color filter strips, determining the type center of each of said" filter strips by finding the point of maximum light transmission through said filter for least one color filter on a transparent support member,

determining the center of said color filter by measuring light transmission through said filter, and depositing a conductive member on said center.

4. The method as in claim 3 wherein the center of said color filter is determined by measuringthe minimum light passing through said filter using light of a color which said filter is designed to reject.

5'. The method as in claim 3 wherein the center of said color filter is determined by measuring, the maximum light passing through said filter using. light of. a color which said filter is designed to pass.

6'. The method of manufacturing a target comprising thesteps of'depositing a color filter through a mask onto a support member, determining the center. of said color filter by measuring light transmission through said filter, moving said mask with respect to said filter a predetermined amount from said center, and depositing a second color filter.

7. The method of manufacturing a target for'a television pickup tube comprising the steps of' depositing a color filter through a mask onto a support member, mov-- ing said mask with respect to saidsupport member to a point where the transmission of White light directed through said mask and saidleolor filter becomes constant, and depositing a second color filter'at said point.

8. The method of manufacturinga target. for a television pickup tube comprising the steps. of depositingv a color filter through a mask onto a support member, moving said mask with respect to said support member to a point where the transmission of white light directedthrough said grill and said color filter becomes constant,. depositing on said support member a second colorfilter at said point through said mask, moving said mask with respect to said support member to a point where the transmission of white light directed through said mask and said target becomes a maximum, and depositing through said mask a third color filter on said support member at said last mentioned point.

color filter strips through a first grill, determining. the. center of said strips: by means of light transmission through asecond grill and through.saidicolor'filter.strip-s;

and depositing a different semi-transparent conductor through said second grill onto said center. 10; The method as in claim 9 wherein the center of said" color filter. strips is determined by finding the maximumilight transmission using light of the same color as said filter is designed to pass.

11. The method as in claim 9 wherein the center of said colorfilter strip is determined by finding the minimum light transmission using light of a color said filter is designed to reject.

12; The method ofmanufacturing comprising depositing an element on a support member through a mask, determining the center of. saidelement by means of light transmission through; a" different mask and said element, and depositing a conductive member on said center through said different mask.

13. The method of manufacturing comprising depositin}; a first element on a support member through a mask, determining the location of said element by moving said mask with respect to said support member to a point where light transmission through. said mask and' said element becomes constant; and depositing a second element at said point,

14". The method of manufacturing a target for a pickup tube comprising depositing a first, second and third group of color filter strips in contiguous relation on 'a support member, determining the center of onev of said first group of color filter strips by means oflight trans mission through a grill and through said one of said first group of color filter strips, and depositing a semi-transparent conductive signal strip on said center.

References Citedin the file of this patent UNITED STATES PATENTS 2,600,121 McGee et'al June 10, 1952 2,600,579 Ruedy et-al; June 17, 1952 2,633,427 Dimmi'ck et a1. Mar. 31, 1953 2,727,828 Law Dec. 20, 1955 

1. THE METHOD OF MANUFACTURING A TARGET OF THE TYPE INCLUDING A PLURALITY OF COLOR FILTER STRIPS EACH HAVING A DIFFERENT SEMI-TRANSPARENT CONDUCTOR THEREON, SAID METHOD COMPRISING DEPOSITING ONE OF SAID COLOR FILTER STRIPS THROUGH A WIRE GRILL ONTO A SUPPORT PLATE, DETERMINING THE CENTER OF SAID ONE COLOR FILTER STRIP BY DETERMING A POINT OF MINIMUM LIGHT TRANSMISSION THROUGH SAID FILTER, MOVING THE GRILL WITH RESPECT TO SAID SUPPORT PLATE A PREDETERMINED AMOUNT AND DEPOSITING THE SECOND OF SAID COLOR FILTER, DETERMINING CENTER OF THE SPACE BETWEEN SAID FIRST AND SAID SECOND DEPOSITED COLOR FILTERS BY DETERMINING THE MAXIMUM LIGHT TRANSMISSION POINT THEREBETWEEN, AND DEPOSITING A THIRD COLOR FILTER STRIP ONTO THE CENTER OF SAID SPACE. 